1. Field of the Invention
The invention relates to a polysiloxane-based prepolymer, more particularly to a polysiloxane-based prepolymer having a three-dimensional network structure. The invention also relates to a hydrogel made from the aforesaid polysiloxane-based prepolymer and used for preparation of contact lenses.
2. Description of the Related Art
To improve oxygen permeability of contact lenses, silicone-containing hydrogel material is used in the preparation of contact lenses gradually. U.S. Pat. No. 5,387,632 discloses a contact lens made from a silicone-containing hydrogel material formed from a polymerization product of a monomer mix including (a) an acrylic-capped polysiloxane prepolymer represented by the formula:
wherein A and A′ are independently an ester or amide of an acrylic or methyacrylic acid; R1 to R10 are independently an alkyl, fluoroalkyl, alcohol, ether or fluoroether group having 1 to 10 carbons, or an aromatic group having 6-18 carbons; m, n, and p are independently 0 to 200 with m+n+p being from 23 to 200; and a and b are independently 1 to 10; (b) a bulky polysiloxanylalkyl(meth)acrylate monomer; and (c) at least one hydrophilic monomer.
U.S. Pat. No. 6,586,548 discloses a biocompatible copolymer produced by polymerizing a mixture having (a) at least one monomer selected from the group consisting of itaconates, (meth)acrylates, fumarates, and styrenics; (b) at least one monomer having a POSS compound including an ethylenically unsaturated radical; and (c) at least one ethylenically unsaturated organosiloxane monomer. Although the biocompatible copolymer exhibits superior toughness and sufficient oxygen permeability, the modulus thereof is greater than 1000 MPa, which undesirably reduces wear comfort.
Therefore, there remains a need for a hydrogel that exhibits sufficient oxygen permeability, wettability, and reduced modulus.